linux-kernel - circular locking dependency on shutdown

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Date:	Thu, 29 Jan 2009 19:50:49 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Linux Kernel list <linux-kernel@...r.kernel.org>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Ingo Molnar <mingo@...e.hu>,
	Manfred Spraul <manfred@...orfullife.com>,
	Peter Zijlstra <peterz@...radead.org>, cpufreq@...r.kernel.org
Subject: circular locking dependency on shutdown

Hi,

Every time I shut down my machine with a 2.6.29-rc2 kernel, I get a
lockdep report that scrolls off. I tried capturing it on video, the
relevant frames are here:
http://johannes.sipsolutions.net/files/shutdown-lockdep-images.tar.bz2

Some info I transscribed:

halt is trying to acquire lock
	(&per_cpu(cpu_policy_rwsem, cpu)){---}

but task is already holding lock
	(&cpu_hotplug.lock){--..}

which already yadda yadda

lock chain:
#1	(&cpu_hotplug.lock){--..}
	...
	get_online_cpus
#0	(&per_cpu(cpu_policy_rwsem, cpu))
	...
	disable_nonboot_cpus

stacktrace:
	down_write
	lock_policy_rwsem_write
	cpufreq_cpu_callback
	notifier_call_chain
	disable_nonboot_cpus
	kernel_power_off
	...


johannes

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